Maghemite nanoparticles and ferrous sulfate for the stimulation of iron plaque formation and arsenic immobilization in Phragmites australis

Wetland plants are considered as suitable biofilters for the removal of metal(loid)s and other contaminants from waters and wastewaters, due to their ability to accumulate and retain the contaminants in their roots. The iron plaque (IP) on the root surface influences the metal(loid)s retention processes. The stimulation of the IP development on roots of Phragmites australis by the external supply of a novel synthetic nanomaterial (nanomaghemite, nFe₂O₃) and FeSO₄ (alone or in combination) was studied. An hydroponic experiment was carried out to evaluate the iron plaque formation after external iron addition, as well as their influence on arsenic immobilization capacity. Microscopic and spectroscopic techniques were utilized to assess the distribution of Fe and As in the roots. The addition of Fe stimulated the generation of the IP, especially when FeSO₄ was involved. The nanoparticles alone were not efficient with regard to IP formation or As adsorption, even though they adhered to the root surface and did not enter into epithelial root cells. The combination of FeSO₄ and nFe₂O₃ was the most effective treatment for improving the As removal capacity, and it seems to be an effective way to enhance the rhizofiltration potential of P. australis in As contaminated (waste)waters.